Respiratory masks are used in a wide variety of applications to protect a human's respiratory system from particles suspended in the air or from unpleasant or noxious gases. They are also frequently worn by, for example, medical care providers to prevent the spread of harmful micro-organisms either to or from the user.
Some respiratory masks are formed predominantly from one or more layers of air-permeable material. Such masks generally have a limited useful life, following which they are intended to be discarded, and generally fall into two categories--moulded cup-shaped masks and fold-flat masks. Moulded cup-shaped masks offer the advantage of having a firmly constructed mask body that is spaced from the wearer's face. Moulded cup-shaped masks that are formed from one or more layers of air-permeable material are described in, for example, GB-A-1 569 812 and 2 280 620, and in U.S. Pat. Nos. 4,536,440; 4,807,619; 4,850,347; 5,307,796; and 5,374,458. Fold-flat masks offer the advantage that, if desired, they can be constructed to fold flat for storage, allowing them to be carried in a wearer's pocket until needed and re-folded so that they can be kept clean between uses. A mask of that type, which opens out to provide a cup-shaped air chamber over the mouth and nose of the wearer during use, is described in WO 96/28217 and U.S. patent application Ser. No. 08/612,527. Other fold-flat masks formed from layers of air-permeable material are described in, for example, U.S. Pat. Nos. 5,322,061; 5,020,533; 4,920,960; and 4,600,002.
A respiratory mask that is formed from one or more layers of air-permeable material generally incorporates at least one attached component, most typically a headband or ties by which the mask can be secured to the user's head. The mask may, however, incorporate other attached components including valves, nose clips and face shields all of which are well known. A method that is frequently employed for attaching such components is ultrasonic welding (as mentioned in U.S. Pat. No. 5,325,892), although, for some components, adhesive bonding and mechanical clamping are also known (as mentioned in U.S. Pat. Nos. 5,374,458 and 5,080,094, and in WO 96/11594 and 96/28217).